Heretofore, one common method of sealing an end fitting into engagement with an HPLC elution column has required the use of tools such as wrenches to make up the sealing arrangement, usually with a compression fitting. Such compression fittings are quite reliable for high pressure liquid chromatography and rely on a radially driven metal to metal seal using a cone shaped ferrule driven into a cone shaped recess which squeezes it into radial compression against the HPLC column. While quite reliable when properly made up, they do require the use of tools and can be over tightened or insufficiently tightened depending upon the skill of the operator. It is very difficult to assess whether or not this type of seal has been made up properly, particularly for high pressure operations, i.e. at 5,000 psi or above. Another type of column and end fitting seal for HPLC uses relies on a metal to metal gasket interposed between the end fitting and the column sealing faces. While this provides a reliable seal, it is not capable of being reused if dismantled. For use at lower pressures, reference is made to the cross-referenced U.S. Pat. No. 4,283,280 which is incorporated herein by reference. In that application a hand-tightenable sealing arrangement is disclosed in which a poly tetrafuoroethylene (PTFE) or other plastic end piece forms a gasket laterally extending over each end of the column tube. This piece is subject to cold flow and therefore the design in said application calls for an arrangement in which the PTFE end piece sealing portion is completely contained within a chamber formed in the end fitting into which the column is inserted. This chamber provides a floor and side walls in such close fitting relation to the end piece that cold flow is effectively prevented. The cross-referenced application discloses that a Belville washer interposed between the end fitting and a drive nut permits hand tightening of the drive nut to compress the Belville washer which in turn transmits through a small deflection the required sealing force for medium pressure work. More specifically, that design has been found to work reliably up to 500 psi and is sufficient for many applications. However, it has been found that this design cannot be taken to HPLC pressures (i.e. 5,000 psi and higher) with sufficient reliability. There is, therefore, a need for a column coupler for use in high pressure liquid chromatographic applications.
There is particularly a need for a high pressure liquid chromatographic coupler which has few parts and which can be made up many times to a reliable sealing engagement without any free parts in the arrangement and by a hand tightening operation.